1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a method of estimating the remaining life of a power transmission belt.
2. Background Art
It is common for automobile makers to collect and investigate data pertaining to the life of power transmission belts on engines subjected to road running tests to estimate the remaining life thereof. It is desirable to be able to make a reasonable estimate of remaining life after a relatively short running distance.
This type of power transmission belt is commonly made with a rubber body having short fibers embedded therein. The fibers project laterally between spaced, pulley-engaging side surfaces to increase lateral pressure resistance and reduce rubber wear. The fibers have exposed portions at the side surfaces. Exemplary of such a belt is that shown in Japanese Provisional Patent Publication No. 7-4470, assigned to the assignee herein.
In FIGS. 4 and 5, a V-ribbed belt, as in Japanese Provisional Patent Publication No. 7-4470, is shown at 10. The belt 10 has a body 12 with load carrying cords 14 embedded therein and extending lengthwise of the belt 10. The belt body 12 has an outer surface 16 to which two layers 18 of canvas are adhered. A plurality of, and in this case three, V-shaped ribs 20 are provided on the inside of the belt body 12. The ribs 20 are spaced laterally from each other and extend in a lengthwise direction. The ribs 20 are made from rubber within which short, reinforcing aramid fibers 22 are embedded. The ribs 20 also have embedded therein short, non-aramid, reinforcing fibers 24 which have a wear resistance that is less than that of the aramid fibers 22. The fibers 22, 24 have lengths oriented generally in a lateral direction. The fibers 22, 24 project from 0.1 to 3.0 mm from oppositely facing rib surfaces 26, 28, which surfaces 26, 28 engage complementary surfaces on a cooperating pulley (not shown).
With the belt 10 trained around a cooperating pulley, the projecting portions of the aramid fibers 22 are bent by the pulley against the rib surfaces 26, 28. This reduces wear on the rubber in the ribs 20 by the pulley during use. Further, the projecting portions of the fibers 22 reduce the coefficient of friction between the rubber in the ribs 20 and the cooperating pulley, thereby reducing noise generation resulting from the ribs 20 momentarily sticking on the pulley.
The non-aramid fibers 24 prevent the bent aramid fibers 22 from pressing into the rubber defining the surfaces 26, 28. The aramid fibers 22 thus remain between the rubber in the ribs 20 and cooperating pulleys. If the bent fibers 22 were allowed to embed in the rubber defining the surfaces 26, 28, the sides of these fibers 22 would be exposed, thereby making slippage between the belt 10 and cooperating pulley more likely.
By reason of having the aramid fibers bent without being embedded in the surfaces 26, 28, the belt 10 is allowed to seat more deeply into cooperating pulley grooves, which thereby reduces belt tension, as at initial system set up. After the belt 10 is run for a period of time, the aramid fibers 22 bent by the pulleys against the exposed non-aramid fibers 24 are pinched and eventually severed.
The aramid fibers 22 wear away, as shown in FIG. 5, at roughly the time that the tension of the belt, which reduces as the belt operates, has stabilized. Once the fibers 22 wear away, the coefficient of friction between the belt 10 and cooperating pulleys increases, thereby improving power transmission performance.
To estimate the remaining life of the above power transmission belt 10 using conventional techniques, the surfaces 26, 28 are visually observed. The abnormal conditions of the belt are divided into five different evaluation categories, identified as A-E, as in Table 1, below.
TABLE 1 ______________________________________ Evaluation Coefficient of Category Result of visual observation remaining life ______________________________________ A No abnormality observed. 1 or more B Cracks about one half the height one half of rubber transmission section observed. C Cracks over the height of rubber one quarter transmission section observed. D Rubber transmission section zero broken. E Rubber transmission section zero severed. ______________________________________
A coefficient of the remaining life is determined by dividing the travelling distance until the belt life expires after a particular observation point by the running distance up to the observation point, hereinafter referred to as the "actual running distance".
It is difficult to make meaningful estimations of remaining life when the actual running distance is only a short distance. For example, there are many evaluations which will fall into category A where no abnormality is identifiable by an unmagnified, visual observation. As a result, the coefficient of the remaining life would be estimated as 1 or more, although there is actually a considerable difference in the remaining life.
As an alternative to mere visual observation, it is know to measure the hardness of the rubber in the belt. However, this estimation varies greatly depending upon operating conditions.